322 THE BRAIN OF THE TIGER SALAMANDER 



A paper model of this transverse series was prepared, X 75, each section being 

 drawn on cardboard seventy-five times the thickness of the section and then cut 

 out along external and ventricular surfaces. These sheets, when properly stacked, 

 show the external and ventricular configuration, and upon them details of internal 

 structure were drawn in colored inks. The relevant data about this specimen were 

 published ('35a) in connection with the preparation of the diagram of the median 

 section, shown here as figure 2C (cf. fig. IB). Scales accompanying the diagram give 

 the section numbers, so that any section figured can be accurately located on the 

 projection. This outline has been used as the basis for many diagrams of internal 

 structure in this work and previous papers. Figures 2A and '2B are similar dia- 

 grams, made from the series of horizontal sections illustrated in figures 25-36. A 

 wax model was made from the sagittal Weigert series C (figs. lA and 85). 



Two series of transverse sections of the adult forebrain based mainly on Golgi 

 sections were published in 1927; six of these are here reproduced as figures 95-100. 

 Six sagittal sections of the middle part of the adult brain stem by Rogers' reduced 

 silver method were published in 1936, figures 17-22; and three of these are shown 

 here as figures 102, 103, and 104. Seven pictures of the chiasma region from the 

 sagittal Weigert series C are in figure 11 of 1941. A series of twelve horizontal 

 Cajal sections of the adult follows in this book (figs. 25-36). Serial sections of larvae 

 of 38 mm., prepared by Cajal's reduced silver method, have been illustrated (hori- 

 zontal, '39b, figs. 2-20; transverse, '14a, figs. 4-14, and '39a, figs. 2-14). Somedetails 

 of the development of the external form of the brain and the internal structures are 

 reported in the papers of 1937-41. For meninges and blood vessels see pages 24-27, 

 my papers ('34c^ and '35), Roofe ('35), and Dempster ('30). 



FIGURES AND DESCRIPTIONS 



Figure lA, B, and C'.^Lateral and median views of the brain of adult A. tigrinum, repro- 

 duced from '24a, figures 1, 2, and 3. 



A. — Drawn from a wax model made from sagittal Weigert sections, no. C, collected at 

 Chicago, 111. X 15. The lateral wall of the cerebral hemisphere has been cut away to open 

 the lateral ventricle; compare figure 85 drawn from the same model. 



B. — Median section of a specimen from Colorado. X 10. The dissection was prepared 

 by Dr. P. S. McKibben and drawn by Katharine Hill. Brains of several specimens were ex- 

 posed, fixed in situ in formalin-Zenker, then removed from the head, washed in water, and 

 hardened in graded alcohols before being cut in the mid-sagittal plane. The shrinkage in 

 alcohol accentuates the ventricular sculpturing. 



C. — Key drawing to accompany figure IB. 



Figure 2 A, B, and C. — Three drawings of the median section of the brain stem of the adult 

 prepared by graphic reconstruction from sections. 



A. — This median section is reconstructed from the series of horizontal Cajal sections ilhis- 

 trated in figures 25-36. X 23. Compare figure 2C made from a specimen differently pre- 

 pared. 



The shape of the two specimens is somewhat different, owing chiefly to slight dorsoventral 

 compression of the midbrain and other distortions of the Cajal specimen. Despite these defects, 

 the correspondence of the two median sections is fairly close. The figures of the two specimens 

 are drawn on the same plan, with the important exception that in the drawing of 2C tlie ven- 

 tricular sulci are projected upon the median plane, while in 2A and B the outhiies of the 

 chief cellular areas are thus projected. In general, the sulci mark tlie boundaries of these areas, 

 but this correspondence is not exact, and there is great individual variation in both these 

 features. In the posterior part of the tegmentum isthmi a vertical dotted line marks, somewhat 

 arbitrarily, tlie boundary between its central nucleus and a posterior sector composed of larger 

 cells and transitional to the large-celled component of the trigeminal tegmentum. 



Two drawings based on this reconstruction are shown, with emphasis on different features. 

 In figure 2A the larger subdivisions of this part of the brain stem are demarcated so as to assist 



